1. Field of the Invention
The present invention relates to a surface inspection method and a surface inspection apparatus employed to detect, for instance, foreign matter (or contamination) adhering to a minute cyclical pattern formed on the surface of a test piece, scarring in such a pattern, or defects such as line width error or film thickness error in the pattern, that are particularly ideal in the inspection of semiconductor wafers such as ASICs, liquid crystal display panels and the like. In addition, the present invention relates to a recording medium and a data signal that provides a surface inspection program.
2. Description of the Related Art
When manufacturing semiconductor devices, liquid crystal display panels, thin film magnetic heads or the like, it is necessary to implement an inspection to detect the presence/absence of foreign matter or the like adhering to a fine pattern formed on the surface of a substrate such as a semiconductor wafer or a liquid crystal panel or defects such as line width errors in the pattern at the stage at which a circuit pattern in a specific layer has been formed, at the ultimate stage at which the circuit patterns in all the layers have been formed and the like. In the prior art, this type of inspection is conducted by an inspector by illuminating the test substrate with illumination light originating from a light source referred to as a macro illumination device and visually observing the scattered light and the diffracted light originating from the surface of the test substrate.
However, such a visual inspection is greatly affected by factors such as the skill and experience of the inspector and the inspection environment. Thus, Japanese Laid Open Patent Publication No. H8-75661 discloses an inspection apparatus that identifies foreign matter and the like by receiving reflected light (scattered light and diffracted light) from a test substrate at a photoelectric detector via a light-receiving optical system and performing image processing on a detection signal output by the photoelectric detector.
As explained above, in the inspection apparatus in the prior art, defects and the like in a pattern on the test substrate are detected by receiving light reflected from the test substrate along a specific direction. Thus, the distribution of defects and the like can be detected promptly over the entire surface of the pattern under inspection, since the diffracted light coming from the entire surface of the test substrate can be received at once by the light-receiving optical system as long as the pattern can be regarded as one type of cyclical pattern having a specific, almost fixed pitch over the entire surface of the substrate, as in a DRAM for instance.
However, in recent years, it has become necessary to conduct inspections on devices constituted of numerous different circuit patterns having different arrangements formed in individual chip areas (shot areas) on a semiconductor wafer, such as the so-called logic-ICs and AS ICs (Application Specific ICs). In such a device, a plurality of types of cyclical patterns having different pitches from each other formed on the test substrate must be inspected. Thus, since only the diffracted light from the cyclical pattern having a specific pitch can be obtained if the optical system has a specific positional relationship relative to the test substrate, there is a concern that defects and the like of cyclical patterns having pitches other than the specific pitch may not be detected.
In addition, since a pattern formed on the surface of the test substrate is achieved by etching or CVD method, the pattern on a semiconductor substrate under the process is formed by thin films for resist. Furthermore, already formed patterns are piled in several layers. As a result, the intensity of the diffracted light may become reduced by the thin film interference and the like. Because of this, if an inspection apparatus in the prior art is set to receive only the diffracted light of a specific order, the diffracted light quantity becomes reduced, which poses a problem in that the likelihood of overlooking defects and the like in the cyclical pattern increases.
An object of the present invention is to provide a surface inspection method and a surface inspection apparatus that make it possible to detect defects and the like in one type of pattern or in a plurality of types of patterns formed on a test piece easily with a high degree of reliability and efficiency. A further object of the present invention is to provide a recording medium and a data signal that provide a surface inspection program executed by the surface inspection apparatus.
In order to attain the above objects, a surface inspection method according to the present invention for inspecting a pattern formed at a surface of a test piece, comprises: a first step in which a plurality of inspection conditions that are different from each other are set; a second step in which light from the surface of the test piece is detected by irradiating illumination light onto the surface of the test piece under each of the plurality of inspection conditions; a third step in which a plurality of sets of detection information corresponding to the plurality of inspection conditions are generated based upon the detected light; a fourth step in which a logical OR of the plurality of sets of detection information is obtained; and a fifth step in which a decision is made as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
In this surface inspection method, preferably, in the third step: an image of the surface is formed by condensing at least one of specific diffracted light, scattered light and reflected light from the surface of the test piece under each of the plurality of different inspection conditions; the image is converted to an image signal; and the detection information is generated based upon the image signal.
Also, preferably, the pattern comprises a plural types of cyclical pattern; the plurality of inspection conditions are respectively set in correspondence to pitches of the plural types of cyclic pattern.
Also, preferably, the plurality of inspection conditions are each set by rotating the test piece around a specific axis of rotation to change an angle of incidence of the illumination light onto the test piece and a light-receiving angle of the light from the test piece.
Also, preferably, the plurality of inspection conditions are each set by moving a light source of the illumination light to change an angle of incidence of the illumination light and/or moving a position of a light-receiving device that receives the light from the test piece to reset a light-receiving angle.
Also, preferably, the plurality of inspection conditions are each set in conformance to a order of diffracted light corresponding to a specific pitch of the pattern on the test piece.
Also, preferably, the plurality of inspection conditions are each set by adjusting a wavelength of the illumination light.
Another surface inspection method for inspecting a pattern formed at a surface of a test piece, comprises: a first step in which a plurality of diffraction conditions that are different from each other are set; a second step in which diffracted light from the surface of the test piece is detected by irradiating illumination light onto the surface of the test piece under each of the plurality of diffraction conditions; a third step in which a plurality of sets of detection information corresponding to the plurality of diffraction conditions are generated based upon the detected light; a fourth step in which a condition which is other than the diffraction conditions and is outside design diffraction conditions determined in conformance to the pattern is set; a fifth step in which scattered light from the surface of the test piece is detected by irradiating the illumination light onto the surface of the test piece under the condition other than the diffraction conditions; a sixth step in which detection information corresponding to the condition other than the diffraction conditions is generated based upon the scattered light that has been detected; a seventh step in which a logical OR of the plurality of sets of detection information generated in the third step and the detection information generated in the sixth step is obtained; and an eighth step in which a decision is made as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
A surface inspection apparatus according to the present invention that conducts an inspection of a pattern formed at a surface of a test piece, comprises: a stage that holds the test piece; an illumination device that irradiates illumination light onto the surface of the test piece; a light-receiving device that detects at least one of diffracted light, scattered light and reflected light from the test piece; a drive device the makes it possible to vary at least one of; an angle of inclination of the stage, a position of the illumination device and a position of the light-receiving device, in order to guide the light from the surface of the test piece to the light-receiving device under a plurality of different inspection conditions; and an arithmetic operation device that sets the plurality of inspection conditions, generates a plurality of sets of detection information in correspondence to the plurality of inspection conditions based upon the light detected by the light-receiving device, obtains a logical OR of the plurality of sets of detection information thus generated and makes a decision as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
Another surface inspection apparatus that conducts an inspection of a pattern formed at a surface of a test piece, comprises: a first illumination device that irradiates illumination light onto the surface of the test piece at a variable first angle of incidence; a second illumination device that irradiates illumination light from a light source formed in a slit onto the surface of the test piece at a second angle of incidence larger than the first angle of incidence; a light-receiving device that detects light originating from the surface of the test piece; and an arithmetic operation device that generates first detection information based upon light originating from the surface of the test piece through irradiation by the first illumination device detected by the light-receiving device, generates second detection information based upon light originating from the surface of the test piece through irradiation by the second illumination device detected by the light-receiving device, obtains a logical OR of the first detection information and the second detection information and makes a decision as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
A recording medium according to the present invention has a program employed in a surface inspection apparatus that conducts an inspection of a pattern formed at a surface of a test piece. And the program comprises: a first instruction for setting a plurality of different inspection conditions; a second instruction for detecting light originating from the surface of the test piece by irradiating illumination light onto the surface of the test piece under each of the plurality of inspection conditions; a third instruction for generating a plurality of sets of detection information corresponding to the plurality of inspection conditions based upon the detected light; a fourth instruction for obtaining a logical OR of the plurality of sets of detection information; and a fifth instruction for making a decision as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
A data signal according to the present invention embodied in a carrier wave comprises a program employed in a surface inspection apparatus that conducts an inspection of a pattern formed at a surface of a test piece. And the program comprises: a first instruction for setting a plurality of different inspection conditions; a second instruction for detecting light originating from the surface of the test piece by irradiating illumination light onto the surface of the test piece under each of the plurality of inspection conditions; a third instruction for generating a plurality of sets of detection information corresponding to the plurality of inspection conditions based upon the detected light; a fourth instruction for obtaining a logical OR of the plurality of sets of detection information; and a fifth instruction for making a decision as to whether or not the pattern at the surface of the test piece is acceptable based upon results of the logical OR.
According to the present invention described above, by changing, for instance, at least, either the angle of incidence of illumination light relative to the surface of the test piece or the light-receiving angle at which the light from the surface is intercepted, a plurality of inspection conditions are set so that diffracted light, scattered light or reflected light can be detected under the individual inspection conditions. As a result, even when one type of cyclical pattern is formed on the surface and the intensity of the diffracted light of a given order from the cyclical pattern becomes lower due to thin film interference or the like, the presence of the cyclical pattern can be verified through a detection signal corresponding to the diffracted light generated under another inspection condition. It can be assumed that foreign matter is adhering or a defect is present in an area where the intensities of the individual detection signals are different from the intensities of signals corresponding to other areas. Then, based upon the logical OR of detection information (e.g., provided in the form of binary data) indicating individual defects and the like corresponding to the detection signals of the light detected under the plurality of inspection conditions, the distribution of defects and the like over the entire surface of the test piece can be ascertained.
If there are a plurality of types of cyclical patterns formed on the surface, on the other hand, a plurality of diffracted light fluxes having different diffracting directions are generated. When the intensity of the diffracted light originating from a specific cyclical pattern is low under a given inspection condition, for instance, settings may be made to ensure that diffracted light originating from the cyclical pattern under another inspection condition is received, and then by obtaining the logical OR of the individual sets of detection information, detection of defects and the like in the plurality of types of cyclical patterns can be achieved at once.